Fix observatory tests broken by running dartfmt. Temporarily reverted formatting for evaluate_activ…

runtime/observatory/tests/observatory_ui/mocks/objects/sentinel.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of mocks;
 
 class SentinelMock implements M.Sentinel {
   final M.SentinelKind kind;
   final String valueAsString;
 
-  const SentinelMock({this.kind: M.SentinelKind.collected,
-                  this.valueAsString: 'sentinel-value'});
+  const SentinelMock(
+      {this.kind: M.SentinelKind.collected,
+      this.valueAsString: 'sentinel-value'});
 }